A type of rotary gravure printing machine is well known in which the printing cylinder is mounted with its axis horizontal, and its lowest portion dipping into a pan of printing ink. A doctor blade on the rising side of the cylinder removes ink from the lands, and the top of the cylinder is in rolling contact with a moving web of material, to which the ink remaining in the recesses of the cylinder is transferred. Because of the open pan of ink, solvent evaporates from the ink, and it is therefore necessary to have a complicated system of pipes and pumps to circulate the ink in order to keep it reasonably uniform in consistency and colour. In addition, bubbles may form on the surface of the ink in the pan, which then leave visible flaws in the printing. If it is desired to change ink in order, for example, to print the same pattern in a different colour scheme, it is necessary to drain and clean out the pan, the pipes, and the pumps, as well as to clean the actual printing cylinder. That necessitates stopping the printing machine for a considerable period of time, and the loss of a significant amount of ink, which may be expensive, and generates substantial quantities of wash liquid contaminated with ink, all of which must be disposed of properly.
U.S. Pat. No. 2,177,656 proposes a gravure printing press in which the ink is applied directly to the cylinder under pressure from within an elongate, hollow applicator assembly, the surplus ink being scraped off and recirculated by means of an adjacent doctor blade. A system of pipes and pumps is provided to ensure a constant supply of ink at the applicator.
There has recently been introduced a gravure printing machine in which ink is fed onto the upper side of a doctor blade on the descending side of the cylinder. The ink is delivered at a single point, at the center of the doctor blade, and allowed to spread freely along the blade.
The present invention provides a rotary printing machine comprising a carriage that is arranged to reciprocate along the cylinder, and to carry a device arranged to deliver ink directly along the surface of the cylinder or along a doctor blade acting on the cylinder.
The present invention also provides a method of rotary printing that comprises delivering ink directly along the surface of the cylinder or along a doctor blade acting on the cylinder by means of a device carried by a carriage that is arranged to reciprocate along the cylinder.
The invention is especially applicable to gravure printing.
The carriage preferably also carries one or more devices arranged to clean the cylinder and/or to clean one or more doctor blades arranged to act on the cylinder, which cleaning devices may comprise means for dispensing a jet or spray of fluid. The cleaning devices advantageously dispense a jet or spray of liquid for cleaning, followed by an air jet to remove excess cleaning liquid.
The carriage may be arranged to carry a reservoir of ink to supply the ink delivery device, preferably by gravity so that no pumps are needed. Instead, such a reservoir could be mounted separately.
The ink delivery device and its reservoir, together with any connecting pipework, are advantageously arranged to be mounted on and removed from the carriage as a unit, to avoid the need to clean them out in situ. Preferably, the carriage is arranged to carry two ink delivery devices, each of which can be replaced while printing is taking place using ink from the other. That avoids the need to change the ink unit during the wash cycle, thereby further simplifying and shortening the wash cycle.
The present invention also provides a rotary printing machine comprising two devices, each arranged to deliver ink directly to the surface of the cylinder or to a doctor blade acting on the cylinder, each of which devices can be replaced while printing is taking place using ink from the other.
The present invention further provides a method of rotary printing comprising delivering ink from two devices in succession directly to the surface of the cylinder or to a doctor blade acting on the cylinder, and replacing one of those devices while printing is taking place using ink from the other.
The invention is especially applicable to gravure printing.
The printing machine may comprise a device extending the length of the cylinder for cleaning the cylinder, in addition to any cleaning devices on the carriage. Such a cylinder-cleaning device may comprise a trough extending the length of the cylinder under the cylinder, and one or more fluid spray or jet devices in or above the trough and, like the rest of the apparatus, is preferably arranged to operate without needing a human cleaner near the moving parts of the machine.
One form of printing apparatus constructed in accordance with the invention, and a method of printing in accordance with the invention, will now be described by way of example only with reference to the accompanying drawings, in which: